The present invention relates to optical scanners and more specifically to a focus changing apparatus and method for optical scanners.
Optical scanners are well known for their usefulness in retail checkout and inventory control. Optical scanners used in inventory control generally employ a laser diode, the light from which is focused and collimated to produce a scanning beam. A mirrored spinner directs the beam against a plurality of stationary mirrors, and collects the beam after it is reflected by a bar code label. A motor rotates the mirrored spinner, and a detector receives the returning beam. The pattern produced by such a scanner is characterized by lines oriented at various angles to one another.
The depth of field of such an optical scanner is determined by factors such as motor speed, aperture size, beam speed, and bar code label spacing and dimensions. Attempting to increase depth of field by varying these factors has not proven effective and may degrade scanner performance. Changing the focus by moving the focusing lens or changing the optical path length has proven ineffective as well.
An optical scanner having an increased depth of field is desirable, especially in inventory management, because it would allow a wider range of article sizes to be scanned with the same probability of reading their attached bar code labels.
Therefore, it would be desirable to provide an apparatus for significantly increasing the depth of field of an optical scanner over previous scanners.